The present invention relates to an apparatus for reducing the toxic components in the exhaust gas of internal combustion engines by influencing the mass ratio of the fuel-air mixture supplied to the internal combustion engine, effected by varying the keying ratio (duty cycle) of a cyclically actuated electromagnetic valve disposed in the control pressure circuit of an engine fuel supply system. The electromagnetic valve is controlled by a regulating device in response to data from measuring transducers which monitor various operating parameters of the internal combustion engine, in particular by an oxygen sensor located in the exhaust system.
In this known system, a sawtooth generator produces a sawtooth voltage of constant frequency and amplitude which is used to vary the keying ratio of the electromagnetic valve. The sawtooth voltage is superimposed on a constant voltage, characteristic of engine operating parameters, and is applied to the inverting input of a summing amplifier of the regulating device. A predetermined voltage, derived from a voltage divider, is applied to the non-inverting input of the summing amplifier.
An apparatus of this type is intended to automatically provide a favorable fuel-air mixture for all operating conditions of the internal combustion engine so as to burn the fuel as completely as possible and thus to prevent toxic gases from being produced, or, at least, to considerably reduce the amount of toxic gases while obtaining maximum performance of the internal combustion engine or minimum fuel consumption, as desired. For this purpose, the quantity of fuel must be very accurately metered out in accordance with the requirements of each operating state of the internal combustion engine and the air-fuel ratio must be varied as a function of engine operating parameters such as speed, load, temperature and exhaust gas composition.